Kids or teens whoever it is, do not insult them publicly or at home. Not every child's mental strength is the same. When someone insults their child in front of others, it crushes them from inside. They feel very low about themselves. It destroys their self confidence. They feel very shocked and they also do not understand what to do then.
Some children or teen donot really mind these. They just forget it and move on. But you have to keep in mind that not everyone is same. There are people who are really sensitive about this things. If you insult your children like that they also do not understand to whom they can talk about this. Because his/her parent might be only person they are close to. Then their mental situation becomes worse.
Nothing good actually comes from shaming or insulting your child like that. If you think it will encourage them to do better in future then youa re totally wrong. It just exploits all the confidence and good feeling they had about themselves and they get drowned in a sea of dark feelings. They feel helpless. They cannot find anything to hold on. These things make them hate their parents and family. They might even get in touch with drugs. They lose all their inspirations to do any good work. It also teaches them to insult other people without considering their situation.
So try not to insult your child. Make them feel good about themselves. Celebrate their small achievements. Believe me, it will inspire them to do something better in future. Be proud of them and they will try to protect your pride with their heart and soul. If they fail in anything, encourage them to win the next time. Teach them not to stop. This will make them a better human. This will make them think that their best friend is their parents. This will increase their respect and love for their parents and make them better human beings. Lets spread love.